Thursday, June 30, 2016

Season 9, stage 2, rounds 10-12

Table after 12 rounds:

The draw rate is 56/96 (58%), still dropping. There were many decisive games in the last three rounds, even most of the draws are interesting. 
We have seen two Chiron crashes in rounds 10-12, one in an obvious winning position. Fire was on fire with 3 wins, it is now in second place. Houdini suffered two losses and is now level with Stockfish.
The table suggests that the engines below Nirvana are less likely to qualify in the top 8 places. On the other hand there are still many games to play and anything can happen.

Some of the game highlights

Raptor had an advantage over Stockfish, and to get out of trouble Stockfish gave a rook for a bishop. This got Stockfish's eval to zero but Raptor was confident it was better, its eval stayed high as the pieces were exchanged. In the R vs B ending Raptor's eval jumped above 4, with no tablebase support it wasn't aware that the 6-man position was a draw. We had to wait for the 50-move rule.

Houdini got into trouble against Fire, a bit unexpected. It had a trapped bishop and an exposed king, and the pressure and evals were rising. Fire just directed its pieces at the white king, and at the right moment attacked. It came out a rook ahead, winning the game. It looked too easy, especially against Houdini. The rematch will be interesting.

Ginkgo was a pawn up early against Vajolet2, as well as a strong bishop pair. Ginkgo exchanged down to RBB vs RBN and won another pawn. Winning became straightforward, it took some time but Ginkgo made it look easy.

Komodo - Jonny was very interesting since Jonny had good results so far but playing Komodo can be frightening. Komodo had an eval advantage in a closed position, and the evals were over 1 when the position opened through a series of exchanges. The game reached a R vs B ending with two extra pawns for black, I expected Komodo to win with such an eval. However, Jonny was able to hold the position for a long time, and the game reached a drawn 7-man position. Jonny is now officially an engine to look out for this season.

Protector held off Rybka's attack and equalized the game. Unfortunately for the viewers the RB vs R ending was misjudged by both engines as a big advantage for white, and we had to wait for the 50-move rule to prove them wrong.

In Chiron - Gull Chiron had the advantage but Gull defended well. They reached an opposite bishop ending with white a pawn up, a sure draw which Chiron misevaluated, and then for no reason Chiron crashed. A similar thing happened in stage 1, Gull gets a bonus 0.5 point.

Hannibal - Andscacs started with a series of exchanges that left Hannibal down a bishop for a rook but ahead on eval. Andscacs' queen side was undeveloped and its queen was harassed by white's pieces. Andscacs gave the material back in an attempt to relieve the pressure, but Hannibal was in a won position, one of the shortest wins in the stage.

Andscacs bounced right back in the game against Raptor. Andscacs had an eval advantage and was a pawn up, but the crucial moment came when it gave a rook for a knight and a strangle hold of the black king. After a series of exchanges the position was a BN vs N endgame, and the game was stopped in a zugzwang leading to the collapse of the black pawn line.

Rybka was a pawn up against Chiron, with connected passers on the queen side. Chiron tried to block the pawns and keep the position closed, but Rybka was able to exchange pieces and reach a winning endgame. That was Rybka's first win of the stage.

Fire was a pawn up against Ginkgo, with connected passers on the queen side. After many exchanges Ginkgo chose to give a rook for two knights, leading to a RR vs RNN ending. The pawns started to march and Ginkgo coulnd't stop them, another win for Fire (second in a row).

Raptor - Houdini got into a RR vs RB ending and seemed to be heading for a draw. The only advantage Houdini had was a pair of connected passers in the center. Raptor saw an opportunity to take the black bishop, but in return Houdini got another passer and moved its king and rook forward. The game reached a 6-man tablebase win for black, Raptor not realizing this with no tablebase support.

Playing black against Naum, Fire attacked the white king with pawns on the queen side. As a result Fire took a rook for a bishop and also boxed the king in the corner. This became a serious back rank mating threat which Fire used to win material and the game. Three wins in a row for Fire, wow.

Komodo was happy when Vajolet2 offered RB for its queen. Vajolet2 thought it was equalizing but in fact this led to a won pawn endgame for Komodo. Don't mess with the lizzard !!

Protector held an eval advantage over Nirvana from the opening but somehow (Protector inaccuracies?) Nirvana found a way to turn the game around to its favor. It attacked the white king with all available pieces until Protector couldn't move at all. Adding one pawn to the attack was all it took to break the white defence, reaching a won RR vs RB endgame.

Chiron outplayed Jonny, with some help from the opening. The game reached an opposite colour bishop ending, Chiron with three extra pawns. This was enough for a win, but then Chiron crashed again. Such a disappointment for the viewers, Jonny lucked out of a first loss in the stage.

Andscacs had a better pawn structure than Gull, and after several piece exchanges this became an eval advantage and an extra pawn in a QR vs QR position. After queens were also exchanged Andscacs had a three pawn advantage in a rook ending, easy win.

Featured game: Stockfish - Houdini
Stage 2, round 11
Link to game on TCEC

This was the first game of the stage featuring two top-3 ranked engines (Komodo hasn't played either of these engines yet). Houdini had just lost its first game of the stage, while Stockfish was still unbeaten but was not performing as well as was expected.

After 30 moves the position was not clear. Material was equal, Houdini seemed to be defending and it had a worse pawn structure. Could Stockfish find a way to improve its position?

Ten moves later Stockfish had a solid eval advantage, a pawn up with two potential passers. There were still many pieces on the board and Houdini is a tough defender, the white king was also exposed to attacks. Tension was running high. The game continued with exchanges that simplified the position until only RB vs RB were left.

The evals were up but the opposite color bishops raised doubts about whether Stockfish could really pull this off. It was far from easy, but the evals gradually grew until the game was adjudicated.

Houdini could hardly move and its bishop could not see the white pieces. The win was not obvious but both engines saw a queening in their PV. Well done Stockfish.

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